The body mass index is calculated from someone’s height and weight (see nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm for a BMI calculator). People with a BMI less than 18.5 are considered underweight, 18.6 to 24.9 is a healthy weight, 25 to 29.9 is overweight, over 30 is obese and over 40 is severely obese.Another method simply measures your waist circumference; over 40 inches in men and over 35 inches notes too much abdominal fat, and this is associated with the health problems of being overweight.

If you are overweight or obese, you are not alone! Using BMI as the definition, 35 percent of adults over age 20 are overweight and an additional 35 percent are obese. Almost 20 percent of kids 6 years old through their teens, and twelve percent of kids under age 6 are obese.

Being overweight, and especially being obese, increases the risks for many diseases. Obesity increases the risk of heart disease, stroke, high blood pressure and diabetes (as well as insulin resistance and the metabolic syndrome). Obesity is also a risk factor for colon, uterine, gallbladder, kidney, esophageal, breast, and other cancers. Other diseases, such as gallbladder disease, depression, lung disease, osteoarthritis and sleep apnea are also more common in overweight people.

Overall, not being a healthy weight increases the likelihood of dying. Plotting the number of people per thousand who die each year for any given age yields a “U” shaped curve; people who are too thin or who are overweight/obese have a higher risk of dying.

Obesity also takes its toll on quality of life; obese people may not be able to do all the activities they would like, and even simple things like sitting in a car or flying on an airplane (with those ever-shrinking seat sizes) can be uncomfortable. Sexual problems, shame, guilt, social isolation and lower work achievement are also associated with obesity.

Why are so many Americans overweight? We:

Eat too much.Eat the wrong foods (junk food makes up 25 percent of the average American’s diet).Have bad eating habits (we eat too fast, at the wrong times of day and for reasons other than being hungry such as because we are bored or having an emotional day).Do not exercise enough.

Although there are some medications that may help people lose weight, there is no magic pill. And since bariatric surgery is only appropriate for a small percentage of people I will not discuss it in today’s column.

My advice for most people is:

Change what you eat: Manage your portion size (to manage your total daily caloric intake) and eat healthier foods. Plan your meals, and then stick to your plan! Note I am not advocating a low-carb, Mediterranean or other specific diet. The best plan is one you can stick with, but the themes of reducing calories and eating healthier is universal (in a normal adult about 10 kcal per pound, plus or minus about 20 percent, will maintain someone’s present weight, so less than that will cause weight loss). For an average person cutting 500 calories per day will allow them to lose a pound a week.Improve your eating habits: Eat only at the table (cutting out snacks), and only when you are hungry. Eat slower to give your body a chance to “feel full," and plan your meal times.Exercise: be sure you check with your health-care provider to be sure exercise is safe and appropriate for you, but if it is 30 minutes of exercise five to seven days per week is recommended.

Sticking with a diet and exercise plan is hard; join a group or simply find a like-minded friend to support you. Keeping the weight off once you have lost it is also a challenge; after losing weight your caloric needs decrease, so the changes you made to lose weight may max out and only allow you to maintain your weight. Most people do gain back some weight (often too much and even all) because they go back to their bad habits (poor food choices, poor eating habits and lack of exercise), so the changes you make must be lifelong lifestyle changes.

The New Year is here and there is no better time to start a campaign to lose those extra pounds and have a happier and healthier 2017. Good luck!